310 The Feeding of Animals 



the available energy of the rations and of the milk was 

 determined. The figures reached were approximately 

 as follows : 



Cow 10 Cow 12 



wt, 775 Ibs. wt. 1,200 Ibs. 



Cal. Cal. 



Available energy of ration 27,120 31,300 



Energy of milk solids 8,450 10,200 



Energy not used in milk 18,670 21,100 



Maintenance needs of resting animal. . . 10,100 13,700 



Balance of energy not accounted for . . . 8,570 7,400 



This energy not accounted for, amounting with the 

 two cows to more than one -fourth the total available 

 energy of the rations, may properly be charged to the 

 work of milk formation. Science and practice agree 

 in naming 15.5 to 16.5 pounds of digestible organic 

 matter as approximately the proper daily amount of 

 digestible nutrients for economical milk production 

 with a good cow of average size, much less than which 

 is not to be considered as generous feeding. The nec- 

 essary supply of nutrients will vary somewhat accord- 

 ing to the size of the cow, but the gradation of 

 quantity should by no means be directly proportional 

 to live weight. Productivity independent of size is a 

 controlling factor. In general small cows eat propor- 

 tionately more food than larger ones. 



The question now arises, What proportion of this 

 quantity should be protein ? The actual amount of 

 proteids in our thirty pounds of average milk is about 

 one pound. If .60 pound is needed daily for mere 

 maintenance as in the case of the steer, we can see 

 where 1.6 pounds of protein must be used, a quantity 



